In a battery module in which battery blocks in which a plurality of battery cells is connected in parallel are connected in series, a fuse that is connected in series to each of the battery cells and that is used for breaking an over current blows when an excessive current flows, and blocks a path. In each of the battery blocks, when many fuses blow, amounts of currents flowing into others of the battery cells in which no fuse is blown increase, and the increased amounts of currents burden the others of the battery cells. A system for detecting a blown fuse is therefore required.
For example, a possible idea is to detect a voltage at both ends of a fuse to detect whether the fuse is blown. However, when many battery cells are used, increases in a number of wires used, a circuit area, and a cost become significant. Another possible idea is to detect whether a fuse is blown based on a relationship between an amount of change in a State Of Charge (SOC) in a battery block and an assumed amount of change in an SOC when no fuse is blown (for example, see PTL 1). However, when obtaining an SOC through a current integration method, a method for detecting whether a fuse is blown based on an amount of change in SOC could be affected by an error when measuring a current.